<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <p id="p">hello</p>
    <button id="btn">change</button>
    <script>
        let p=document.getElementById("p");
        let btn=document.getElementById("btn");
        btn.onclick=function(){
            p.innerHTML="改变了";
        }
    </script>
</body>
</html>